Fabrics with leno weave show specific properties resulting from the different construction of the crossing point, the crossing proper and, consequently, the thread interlacing being achieved by the mutual turning of two warp threads around each other thereby eliminating the need to interlace the weft with said warp threads. In each weaving cycle, its position is each time over one and the same, and under the other, of the warp thread systems, said warp threads bringing about the interlacing effect not by mutually alternating the upper and the lower position but by their mutual turning around each other.
Thus, the warp threads are divided into two groups, i.e., into the stationary and the rotating ones. Special mechanisms are required to generate their mutual movement normal to their axis.
The known embodiments of such devices contain special leno heddles and return motion half-heddles.
Another embodiment makes use of shaft frames equipped with needles instead of with heddles. Here, the shaft frames, in addition to their shed forming motion, carry out a mutual reversible motion parallel with the direction of the shed insertion.
Another known method of leno weave creation is described in the patent CZ No. 280643 relating to a device for binding the fabric edge on weaving machines. Its advantage over the preceding ones consists in the method of generating the required motion of the rotating warp threads by means of an oblique slot provided in the shaft frame carrying out the standard shed motion so that, unlike the preceding embodiment, the shaft frame need not move in two directions and, consequently, the arising dynamic forces are substantially reduced, and the mechanism is simplified. In comparison with the embodiment using special heddles, this embodiment contains no further components such as half-heddles for mediating the positive contact with the warp threads and whose motion shows discontinuous changes during the heddle frame alternations that by their impacts have adverse effects on the operation frequence of the weaving machine. However, the drawback of the mechanism described in the patent CZ 280643 consists in that it permits to produce the leno weave only with a limited number of warp threads on the fabric edge, and not a complete leno fabric.
Another drawback of the described embodiment consists in that it fails to ensure the same tension in each of the two warp thread systems, and consequently, in the uneven proportionate elongation during the weaving process. For this reason, warp threads to be interlaced in this way must be supplied from special accessory warp thread bobbins, each of them equipped with an independently adjustable brake.
Another well-known device for producing the gauze weave on the fabric edge is described in EP 152 956 A2 and EP 450 120 A1, intended for double gripper looms for weaving double fabrics. For producing the edge on each fabric, it comprises one system of stationary threads, and two systems of laterally deflectable movable threads. The movable threads are led across oblique grooves responsible for their movement like in the preceding solution, and the stationary threads are led from supplementary warp bobbins into the eyes of the vertically movable threads while passing through a guide aperture provided in the needle holder situated outside the longitudinal axis of the needle so that the rotating threads are spliced/interconnected with each other only in the front shed, i.e., in the section between the beat-up point and the needle's eye, but are permanently separated from each other in the section between the guide aperture in the needle holder and the warp bobbin. After passing through the guide aperture, the stationary threads make a turn of 90.degree. and pass along the needles into the needle eyes from the needle front side to the needle rear side after which they again arrive at the needle front side. The drawback of this solution consists in particular in great strain imposed on the stationary threads so that the device can be used only for the creation of the fabric edges where the warp threads are supplied from special supplementary warp bobbins with individual adjustment of the thread tensions or with the thread tension adjustment carried out separately for the stationary threads on the one hand and for the movable warp threads on the other hand.